Printing methods or etching methods are known as methods for forming a conductive pattern of conductive circuits, electrodes, and the like used in touch panels, electronic paper, and numerous electronic components.
Formation of a conductive pattern by the etching method requires the following process: a patterned resist film is formed by photolithography on a substrate on which a variety of metal films are formed by vapor deposition; subsequently, the unnecessary part of the vapor deposited metal films is removed by chemical or electrochemical dissolution; and finally, the resist film is removed. Thus, this process is remarkably complicated, and the productivity is poor.
The printing method allows mass production of the desired pattern at a low cost. Furthermore, conductivity can be easily provided by drying or hardening the printed coating film.
Flexographic printing, screen printing, gravure printing, gravure offset printing, inkjet printing, etc. have been proposed as these printing methods in accordance with the line width, the thickness, and the production speed of the pattern to be formed.
As the printed pattern, the formation of a high-resolution conductive pattern having a line width of 50 μm or less has been demanded from viewpoints such as the miniaturization and improvement of design of electronic devices.
Further, in view of the increased demands for reduction of the thickness, weight savings, and flexibility of electronic devices, and roll to roll printing having a high productivity, conductive inks in which high conductivity, substrate adhesion, film hardness, etc., can be obtained by printing on a plastic film and firing at a low temperature for a short period of time have been demanded. Furthermore, there has been a demand for conductive inks that can provide the above-mentioned properties when printing, among plastic films, a low cost, high transparency PET film or a transparent conductive film in which an ITO film is formed on a PET film.
Under such circumstances, a thermosetting electroconductive paste composition containing a silver powder, a thermosetting component, and a solvent, the thermosetting component including a blocked polyisocyanate compound, an epoxy resin, and a curing agent selected from the group consisting of amines, acid anhydrides, and imidazoles is known (PTL 1). However, there are the drawbacks that, because the firing temperature is 150° C. and an isocyanate reaction catalyst is not contained, the curing temperature is high, and because the blocking agent of the isocyanate is MEK oxime, the firing time is long.
Further, a conductive paste composition containing an organic binder resin, an electroconductive powder, a colorant, an organic solvent, and a crosslinking agent, wherein the number average molecular weight of the organic binder resin is in the range of 3000 to 50000 is known (PTL 2). This technology, in the same manner as the technology of the aforementioned PTL 1, also has the problem that, because the firing conditions are 130° C. for 30 minutes and an isocyanate reaction catalyst is not contained, the firing time is long, and because the blocking agent of the isocyanate is MEK oxime, the firing time is long.
Furthermore, a conductive paste composition containing an organic binder resin, an electroconductive powder, a colorant, an organic solvent, and a crosslinking agent, wherein the electroconductive powder contains a powder having a spherical form and the content of this powder is 50 to 95 mass % relative to the entire amount of the electroconductive powder is known (PTL 3). This technology has the same problem as the aforementioned technology.
PTL 1: Japanese Unexamined Patent Application Publication No. 2002-161123
PTL 2: Japanese Unexamined Patent Application Publication No. 2009-26558
PTL 3: Japanese Unexamined Patent Application Publication No. 2009-24066